1. Field of the Invention
This invention relates to a device for connecting a fan to the inlet of a face mask filter to generate an overpressure (i.e., a pressure in excess of atmospheric pressure) in the face mask filter and in a face mask attached to the filter. The device includes an adapter having means for fastening it to the face mask filter and an air duct leading from the fan to the inlet of the face mask filter.
2. Description of the Prior Art.
A connecting device of this type is disclosed in United Kingdom patent GB-A-560,877. That device has a fan with an electric motor which sucks in air through openings in a housing and transports it through a filter to a face mask. An overpressure is created by the fan in the face mask which assists the breathing of the person wearing the face mask. However, this device is not suitable for the commercial canister filters which are generally used.
A similar device is disclosed in German patent DE-A-3,623,269. The device includes an adapter which is made of a flexible rubber and has a tubular extension into which a canister filter can be inserted. A particular disadvantage of the device is that it comparatively difficult to insert the fan into the adapter, when the adapter has elastically expanded, and to remove it. Periodic cleaning of the fan which is necessary with such a device is therefore very complex, time-consuming and expensive. The comparatively long and large ventilation duct between the inlet of the filter and the outlet of the fan is an additional disadvantage.